A wide variety of communications alternatives are currently available to telecommunications users. For example, facsimile transmission of printed matter is available through what is commonly referred to as a stand-alone fax machine. Alternatively, fax-modem communication systems are currently available for personal computer users which combine the operation of a facsimile machine with the word processor of a computer to transmit documents held on computer disk. Modem communication over telephone lines in combination with a personal computer is also known in the art where file transfers can be accomplished from one computer to another. Also, simultaneous voice and modem data transmitted over the same telephone line has been accomplished in several ways.
Modem technology has recently multiplexed the transmission of various nonstandard data with standard digital data, such as voice over data communications, creating a hybrid datastream of voice and digital data.
One problem associated with voice over data communications occurs when two users initiate an analog voice connection and subsequently wish to initiate digital data or voice over data communications. One method to initiate digital data or voice over data communications is to terminate the analog voice connection and re-connect in a digital data or voice over data format, however, this is inconvenient and requires hanging up and redialing between the users.
A time-division multiplexing voice and data communication system which switches between a "SYSTEM mode" and a "POTS mode" was proposed in U.S. Pat. No. 4,740,963 by Eckley, entitled "VOICE AND DATA COMMUNICATION SYSTEM". In SYSTEM mode a multiplexer means time-division multiplexes a compressed, digitized analog voice signal with a digital data signal to produce a composite digital signal having a data rate substantially equal to the uncompressed, digitized voice signal. The POTS mode is the analog voice mode. A remote user unit switches to the SYSTEM mode upon receipt of a particular dual-tone multifrequency (DTMF) signal from a remote digital loop carrier unit. The Eckley system returns to POTS mode upon detection of a failure of a remote user unit or upon detection of a particular code from a central office terminal. The Eckley invention requires a special mode tone detector to generate a control signal to enter SYSTEM mode and a code detection circuit to detect the particular code to return to POTS mode. However, the Eckley system is designed to operate in a particular voice and data time-division multiplexing system.
Packetized voice over data communication systems utilize several communication parameters not found in fixed time-division multiplexing systems and require negotiation of packet transmission parameters, such as speech compression ratio and speech algorithm selection.
Therefore, there is a need in the art for a mode switching control for a packetized voice over data communications which provides a plurality of switching means for transferring between an analog voice connection and digital data communications or voice over data communications without having to hang up on the original analog voice connection. The mode switching control should provide means for negotiating digital data and voice over data communications parameters.